Many different instrumental techniques are commonly used to accomplish spectroscopic analysis. Hitherto, two-dimensional monochromatic images have been obtained mainly by thin-film filter systems, narrow-bandpass tunable interferometric monochromators, and wide-slit spectrographs.
Thin-film filter systems and monochromators usually require narrow bandpass thin film filters as prefilters. Since these prefilters are tunable over only a very limited spectral range, these systems do not permit simultaneous observations of multiple emission lines spread over a large spectral range.
The wide-slit spectrographs produce multiple emission line images across a broad spectral range. However, the wide-slit which permits two dimensional imaging also results in a corresponding degradation in spectral and spatial resolution. This spectrograph also suffers from image overlap when it is used to image closely packed emission lines.